where <remote-system> is either the IP address or its hostname including domain as in bren.hih.au.dk - if using a different username than the one you're logged in with on current system use <username>@<remote-system>

Using SSH to get around

Thanx to this page it is easy to collect useful examples of extensive usage of ssh.

Here are examples of copying from local to remote and the other way around.

and you'd like to login in just a few keystrokes. Is that possible? Yes!

You can login in one command. Follow these instructions to set-up up your Linux. If you're running Apple (which is FreeBSD down below) it is probably something alike, but there may be differences. Windows user: Installing the full Cygwin should enable you to prepare at set-up alike.

The first two lines specifies that you want to reach the host bren at bren.hih.au.dk (because this is not a public address you'll need to have it define locally in your /etc/hosts or in your local DNS. Alternatively you can replace the URL with the IP address directly.

The next two lines tells us, that when accessing my-devhost, we shall use ssh to connect to bren and as user <user>, next the nc command is used to jump to the dev-host at the 10.1.18.nnn address on port 22 (replace nnn with your specific number).

In this particular case I login in on my home PC as klaus not klausk, so when establishing a connection to my-devhost I issue

$ ssh klausk@my-devhost

which will bring me directly to the devhost using bren as a jump stone.

You can use the ssh-copy-id to send your ssh keys directly to the devhost and thereby login without being prompted for your password.

After upgrading ssh

Keyboard issues

If the keyboard doesn't work correctly (typically the arrow, pagup/dwn, etc keys) execute this in a NX session console:

setxkbmap -model evdev -layout us

change us with your keyboard layout. i.e. dk for Danish.

Session closes

If you encounter that you can login, but the session is immediately closed issue this on the remote server:

$ /sbin/restorecon -v-v/home/<your home dir>/.Xauthority

Slow NX on Windows

From nomacinhe.com I've picked up this advice:

NX can be slow in drawing some elements of KDE desktop
This problem has been verified with NX Client installed on a Windows 7 64-bit connected to an NX session running a KDE desktop version 3.
This desktop environment shows a tool-tip box which appears gradually and then disappears completely when the pointer moves over the elemnts on the task bar.
The drawing of such tool-tips appears slow. While drawing progresses, the NXWin process on the Windows host takes a lot of CPU time (50% on a dual core CPU).
This problem doesn't occur if DirectDraw engine is disabled in NX Client settings. To do it:
Press "Configure"
Chose tab "Advanced"
Check the box "Disable DirectDraw for screen rendering".
This problem has never seen on 32-bit Windows versions.

Howto downgrade a yum-installed package

Lookup the exact version number - maybe in /var/log/yum.log*

Login as root or sudo: (here nx-3.4.0-4.el5.centos.i386 is downgraded to nx-3.3.0-14.el5.centos.i386)

yum downgrade nx-3.3.0-14.el5.centos.i386

To prevent automatic upgrade when yum in run by cron add this to the yum.conf in /etc:

exclude=nx*

Scan a network for occupied addresses

Use nmap.

To scan the 255 addresses for activity in the network 10.1.18.0 use this command.

$ nmap-sP 10.1.18.0/24

Sendmail

In order to let sendmail forward root messages to a human receiver edit the /etc/aliases file and add something like this at the end (only root can do):

root: name@domain.org

where name@domain.org shall be changed to an appropriate mail address.